This invention relates generally to electric motor fuel pumps and more particularly to a regenerative type fuel pump having a vapor vent.
Electric motor regenerative type fuel pumps have been employed in automotive engine fuel delivery systems. Fuel pumps of this type typically include a housing adapted to be submerged in a fuel supply tank with an inlet for drawing liquid fuel from the surrounding tank and an outlet for delivering fuel under pressure to the engine. The electric motor includes a rotor mounted for rotation within the housing and coupled to an impeller of the fuel pump for co-rotation therewith. The impeller typically has a circumferentially array of vanes about the periphery of the impeller with pockets defined, between adjacent vanes. An arcuate pumping channel, with an inlet and an outlet port at opposed ends, is communicated with the impeller periphery for developing fuel pressure through a vortex-like action on the liquid fuel in the pockets and in the surrounding channel. One example of a fuel pump of this type is disclosed in U.S. Pat. No. 5,257,916.
Agitation of the fuel, hot fuel and the relatively low pressure in a low pressure portion of the fuel pumping channel exacerbate the generation of fuel vapor in the liquid fuel within the fuel pump and fuel tank. Undesirably, the fuel vapor reduces the volume of liquid fuel pumped by the fuel pump, can cause vapor lock and stalling of the engine, and causes cavitation and increased noise in operation of the fuel pump. Accordingly, it is desirable to limit the generation of fuel vapor in the liquid fuel pumped by the fuel pump, and to vent fuel vapor from the fuel pump.
U.S. Pat. No. 5,680,700 discloses a regenerative fuel pump having an impeller with a plurality of vapor vent passages formed through the impeller radially inboard of the pockets formed between adjacent vanes of the impeller. Each vapor vent passage directly communicates with a separate pocket and when the impeller rotates the vent passages serially communicate with a vapor vent port through an end plate of the fuel pump to facilitate the discharge or venting of fuel vapor from the fuel-pumping channel.
U.S. Pat. No. 4,591,311 discloses a fuel pump having a vapor discharge port disposed within an enlarged low-pressure portion of its fuel pumping channel. The vapor discharge port is located entirely within the fuel-pumping channel and is relatively small to minimize liquid fuel loss and pressure loss in the pumping channel. Undesirably, the small vapor discharge port disposed directly within the fuel pumping channel is not effective to evacuate all fuel vapor from the fuel pumping channel and a percentage of the fuel vapor flows downstream into the higher pressure portion of the fuel pumping channel reducing the fuel pump efficiency, capacity and performance.
An electric motor regenerative type fuel pump has a vapor vent passage disposed outside of a fuel pumping channel and communicating the fuel pumping channel with the exterior of the fuel pump to vent fuel vapor from the fuel pumping channel. The vapor vent passage extends through one of a pair of end plates between which the impeller is received for rotation. Preferably, the vapor vent passage communicates with the fuel-pumping channel through a connecting slot.
Desirably, the fuel pumping channel has an enlarged cross-section low pressure portion adjacent to its inlet and leading to a high pressure portion of reduced cross-section which terminates at an outlet of the fuel pumping channel from which fuel is discharged under pressure. In the preferred embodiment, the vapor vent passage opens into the fuel pumping channel at the downstream end of the low pressure portion, immediately upstream of the high pressure portion. The vent passage is radially inward of and opens into the radially inner edge of the fuel pumping channel because the greatest concentration of fuel vapor is at the radially inner portion of the fuel pumping channel due to the centripetal force on the fluid in the fuel pumping channel. In another embodiment, the vapor vent passage opens into the fuel pumping channel at the upstream end of the high pressure portion, downstream of the low pressure portion of the fuel pumping channel. In yet another embodiment a transition in the fuel-pumping channel defines a vapor diverter which directs fuel vapor to the vapor vent passage to improve the venting of vapor from the liquid fuel in the fuel pump. In each embodiment, the vapor vent passage preferably extends through a pump plate spaced from a groove in the pump plate which defines in part the fuel-pumping channel. A connecting slot preferably communicates the fuel-pumping channel with the vapor vent passage.
Objects, features and advantages of this invention include providing an electric motor regenerative fuel pump which has improved venting of fuel vapor therefrom, utilizes a vapor vent passage disposed outside of a fuel pumping channel, reduces fuel vapor pumped and discharged from the fuel pump outlet, reduces cavitation and noise of the fuel pump in use, enables the fuel pump to be operated at low speed, enables use of electronic control of the speed of the fuel pump motor, improves efficiency of the fuel pump, improves hot fuel handling of the fuel pump, is of relatively simple design and economical manufacture and assembly, and in service has a long useful life.